Convert Carat to Stone (ct → st)

Converting carats to stones is straightforward: multiply by the conversion factor. Follow these three steps to do it by hand or in your head.

1. 1
   Take your value in carats

   Start with the number of carats (ct) you want to convert.
2. 2
   Multiply by 0.00003149

   The conversion factor from ct to st is 0.00003149. Multiply your value by this number.
3. 3
   Read the result in stones

   The result is your value in stones (st).

Multiply the value in carats by 0.00003149. For the reverse direction, multiply by 31,751.466.

• ✓1 carat = 200 mg = 0.2 g exactly since 1907.
• ✓Carat (gem weight) and karat (gold purity, 24 K = pure) are different words with different meanings.
• ✓A carat is divided into 100 points; a 0.25 ct diamond is called a "25-pointer".

• ✗Confusing carat (mass) with karat (gold purity).
• ✗Assuming a 2-carat diamond is twice the physical size of a 1-carat — volume scales with cube root of mass.
• ✗Using "karat" on gemstone certificates — international standard is "carat" spelled with a C.

What is the Carat?

The carat equals exactly 200 milligrams (0.2 g) and is the universal unit for gemstone and diamond weight in the global jewelry industry. The word derives from the Greek 'keration' and the Arabic 'qīrāṭ,' both referring to carob seeds, which were once used as natural counterweights for weighing gems because they have remarkably uniform mass. The metric carat was standardized in 1907 at exactly 200 mg, replacing dozens of regional carat values that had varied between 188 and 213 mg. A 1-carat diamond is roughly 6.5 mm in diameter, and the famous Hope Diamond weighs 45.52 carats. The carat is distinct from the karat (with a 'k'), which measures gold purity (24-karat = 100% gold). It relates to the gram (5 ct = 1 g) and the milligram (200 mg = 1 ct). Gem dealers commonly use 'points' for fractions (100 points = 1 carat).

• Diamond and gemstone retail and valuation
• Jewellery manufacturing and design
• International gem certification (GIA, IGI)

What is the Stone?

The stone equals exactly 14 pounds or 6.35029318 kilograms and remains the traditional British unit for personal body weight. Originally based on a stone literally used as a counterweight on a balance scale, the unit was standardized at 14 pounds by an Act of Parliament in 1835. While metrication has reduced its role in commerce, the stone persists in British everyday life — a person is described as '11 stone 4' (158 lb) rather than 72 kg — and is widely used in British and Irish weight-loss programs, medical contexts, and gym equipment. The stone is virtually unknown in the United States and most of the world. It relates to the pound (14 lb = 1 stone), the kilogram (1 stone ≈ 6.35 kg), and the long ton (160 stone = 1 long ton). Stones-and-pounds notation (like '11 st 4 lb') is the British equivalent of decimal kilograms.

• Human body weight in the UK and Ireland
• British medical charts and patient records
• British boxing and wrestling press reports